1. Field of the Invention
The present invention relates generally to quantum communication and specifically to a quantum switch teleportation system using quantum entanglement states to send a quantum state to two receivers, alternatively.
2. Description of the Related Art
Recently, quantum entangled state, hereinafter referred to as “entangled state” has been drawing public attention because it is thought to enable quantum communication and quantum information processing. There are many ways to generate entangled states, such as a non-locally entangled state of the Einstein, Podolsky, Rosen (EPR) type. For example, one method uses optical parametric effects and linearly combing pairs of squeezed states. In addition to single particle entanglement, many photon states of light can be used for quantum information. These states are described by continuous variables.
Quantum mechanics offers certain unique capabilities for the processing of information, whether for computation or communication. It has been demonstrated that an unknown quantum state can be transferred from a sending station to another receiving station by using prearranged entanglement state. Entanglement relates to correlation of these quantum states. The characteristics of the entangled light can be used to, for example, communicate quantum information.
One of the most striking features of quantum information is that it makes quantum teleportation possible. In a quantum teleportation scheme, the quantum state of a system can be transmitted from one location to another location through direct transmission of only classical information, provided that the sender and the receiver share a non-locally entangled state of the EPR type. Thus, quantum teleportation is a type of quantum communication technique.
Quantum communication techniques that use entangled light are described in, for example, in A. Furusawa, et. al., Science, 282, 706 (1998); T. C. Ralph, et. al., Phys. Rev. Lett. 81, 5668 (1998); Jing Zhang, et. al., Phys. Rev. A 62, 064302(2000); C. Silberhom, et. al., Phys. Rev. Lett. 86, 4267(2001); and Y. Zhang, et. al., Phys. Rev. A, 62, 023813(2000). However, these communication techniques disclose a system having only one receiver.
An article by J. Zhang, et. al., in Journal of Optics B, 3 293 (2001) (published on the internet on Aug. 23, 2001), discloses a quantum teleportation scheme in which a quantum state is teleported from the sending station to either of two receiving stations. In this scheme, two pairs of EPR beams with identical frequency and constant phase relation are used to produce two pairs of conditional entangled beams by composing their modes on two beam splitters. One output of a beam splitter is sent to the sending station and the two outputs of the other beam splitter are sent to the respective receiving stations. Which receiving station actually receives the teleported state can be decided by correlating the in-phase or out-of-phase quadrature components of two two-mode squeezed vacuum states. However, this scheme is cumbersome and complicated because it uses two beam splitters and two pairs of EPR beams to produce two pairs of conditional entangled beams.